Why in the News? 

The fourth global coral bleaching event (GCBE4) has become the most widespread and fastest on record, affecting reefs in 74 countries. The global coral bleaching event that began in January 2023 has surpassed previous records. According to the National Oceanic and Atmospheric Administration (NOAA), it is affecting nearly 100% of coral reef areas in the Atlantic and 77% of global reefs. The high heat stress during both El Niño and La Niña phases is responsible for this widespread impact. 

Coral Reefs 

• Definition: Coral reefs are underwater structures made up of calcium carbonate produced by living corals, which are marine invertebrates belonging to the class Anthozoa. 
• Types of Coral Reefs: 
  • Fringing Reefs: Closest to shore, growing directly from the coastline. 
  • Barrier Reefs: Located further from shore, separated by a lagoon. 
  • Atolls: Circular reefs that encircle a lagoon, typically formed from the subsidence of volcanic islands. 
• It supports approximately 25% of all marine species, including fish, invertebrates, and marine mammals. 
• They provide habitat and breeding grounds for many marine organisms. 
• They act as natural barriers, protecting coastlines from erosion and storm surges, thus reducing the impact of natural disasters.

Fourth Global Coral Bleaching Event (GCBE4) 

• It is a significant environmental crisis affecting coral reefs worldwide, driven primarily by climate change. 
• This event is characterized by widespread coral bleaching, which occurs when corals expel the symbiotic algae (zooxanthellae) that provide them with nutrients and color, leading to severe ecological consequences. 
• It began in 2020 and has continued to affect coral reefs globally, marking the fourth such event since monitoring began in the late 20th century. 
• Coral reefs in regions such as the Great Barrier Reef, Caribbean and parts of the Indian and Pacific Oceans have been severely impacted. 
• Causes 
  • Rising Sea Temperatures: Prolonged periods of elevated sea surface temperatures, often linked to global warming, are the primary driver of coral bleaching events. 
  • Ocean Acidification: Increased CO2 levels lead to lower pH in oceans, negatively affecting coral health and their ability to calcify. 
  • Pollution: Nutrient runoff, sediments, and pollutants contribute to the degradation of water quality, exacerbating the stress on coral ecosystems. 
  • The current event has affected reefs in 74 countries and territories, with recent confirmations in Palau, Guam and Israel.